This invention is related to cable television (CATV) and wireless transmission systems. More particularly, the invention is related to an apparatus for merging selected lines of at least two vertical blanking intervals (VBIs) for transmission over the RF band which is typically reserved for a single VBI.
With the increasing array of services from CATV and wireless network operators, it has become imperative for operators to offer more services in the same amount of RF transmission bandwidth. Moreover, wireless pay television systems, whether MMDS or conventional VHF/UHF television, are generally constrained to far fewer channels than the conventional CATV systems with which they compete. The challenge is offering more channels to subscribers within the spectrum constraints imposed by government regulations.
For a typical television program, since the video portion of the program occupies most of the available 6 MHz on an NTSC television channel, much of the research toward maximizing the amount of bandwidth has been traditionally devoted towards compressing and minimizing the amount of bandwidth the video information occupies. Accordingly there exists a need for providing more channel capacity within the same amount of transmission bandwidth while maintaining the quality of the transmitted data.
Ancillary information services are typically transmitted using existing television broadcast channels. The ancillary information is transmitted in the VBI and decoded at a television in order to display the ancillary information along with the television picture. Ancillary information typically includes text, for example closed captioning or related program information. Since the ancillary information transmitted along the VBI does not typically utilize the entire bandwidth assigned to the VBI, it is desirable to merge several VBIs into the bandwidth allotted for a single VBI in order to minimize the overall bandwidth required for the television transmission.
United Kingdom Patent Application No. GB 2286321A discloses a method for data distribution comprising storing packets of data in a random access memory, storing transmission characteristics for each packet, reading the characteristics and transmitting each packet to an audience in accordance with the frequency and timing parameters set forth in the packets' particular transmission characteristics. However, this system does not have the capability of merging the information from several VBIs into the bandwidth allotted for a single VBI.